The present invention relates to web roll shafts having outwardly expansible pressure members that are driven by pressurized hydrogel.
In the web converting industry it is necessary to rotate large (sometimes more than 12 feet in diameter) rolls of web material. To achieve this end web material roll shafts and chucks are used which have a diameter smaller than the inner diameter of a web material roll core for easy insertion but which selectively expands after insertion so that they tightly grip the interior surface of the web material roll core.
The lugs or bladders that are pushed outwardly to create the selective expansion are typically pneumatically actuated. Although hydraulically actuated lugs could place more pressure against the inside surfaces of a web material roll core, hydraulics have typically been avoided in the processing of web materials because of the threat of a hydraulic fluid leak. Such a leak could easily ruin an entire role of paper or other porous web material because the centrifugal force exerted by the web material roll rotation could press the typically oily hydraulic fluid through many layers of web material. Moreover, such a leak could remain undiscovered until the fluid had leaked through to the exterior layer of web material, thereby ruining, for example, an entire roll of paper.
Unfortunately, the limits that the use of pneumatics place on the amount of pressure that can be applied to the inside of a web material roll core, places a limit on the acceleration and deceleration that a chuck may undergo without causing the web material roll to slip. Moreover, the desirability of applying high pressure to the expansion lugs leads to the placement of large pneumatic structures as part of each chuck assembly, because a large diaphragm (or piston) surface area is required to apply a high pressure when using pneumatics, due to elasticity of air, which is far greater than the elasticity of hydraulic fluid. The large structure needed to support a large diaphragm, however, acts as a fly wheel to the rotating chuck, placing an additional limit on the maximum acceleration and deceleration capabilities of the chuck.
An additional problem found in web material production and conversion facilities is that caused by the removal of a pair of chucks from either side of a web material roll. As the chucks are retracted, it is not uncommon for the web material roll to slide off of one chuck before sliding off of the other, simply due to the unpredictable frictional pull of each chuck. When this happens it is possible that the chuck upon which the roll remains will be damaged by the torque applied by the weight of the web material roll. Even if the chuck does not sustain damage some extra labor is needed at that point to remove the web material roll from the chuck to which it remains mounted. This disrupts the smooth flow of web material mill operations.
An additional problem encountered in the use of web material roll shafts is the variability of load demand on the expandable lugs. When a web material roll is close to empty not much lug pressure is needed to maintain control over the roll. On the other hand, too much pressure could burst the web material roll core. When the roll is full, just the opposite set of demands is encountered. A great deal of pressure must be applied to the interior of the roll core to maintain control over rotation and prevent the roll from slipping about the shaft. Moreover, there is little danger of bursting a full roll because of the many layers of web material that reinforce the central core.
What is therefore needed but not yet available is a web material roll shaft with expandable lugs that can be pressed outwards with a force greater than that available with pneumatics yet does not require the bulky apparatus necessary with pneumatics, and does not involve the danger of damaging the web material on the roll that appears to be inherent with the use of hydraulics. Also needed but not yet available is a web material roll chuck that could be removed from the web material roll with certainty so that a pair of chucks could be removed simultaneously without fail. Additionally needed but not yet available is a web material roll chuck that could apply pressure to the inside of a web material roll that would not burst an empty roll but could accurately control a full roll.